Performing maintenance work on rotary flow machines is a time and cost consuming operation due to the multitude of components which has to be disassembled to get free access to the inner parts of the rotary flow machine. Especially in case of gas or steam turbines the rotating and static components being arranged within the gas flow path are directly exposed to hot gas flow by which degradation effects are unavoidable so that maintenance work has to be performed in periodic time intervals.
In general, rotary flow machines of the before mentioned art are typically provided with an inner housing that contains rows of vanes for directing hot gas flow passed the blades mounted on the rotor unit. Such conventional inner housing is disposed within an outer housing for well-known reasons.
For performing maintenance work on such well-known rotary flow machines the inner and outer housing are divided into an upper and a lower housing half that are removable joint to each other. In a similar manner, the vane rows are also divided into upper and lower semi-circular halves so that they may be removed with the associated inner casing half as a unit, and then subsequently removed from the casing for repair or replacement work.
To facilitate maintenance work on such kind of rotary flow machines it is a well known technique to lift off first the upper halves of the outer and inner casing and to rotate the inner casing together with the rows of vanes about its rotational axis to an upper most position in which it is free of the rotor, at which time it may be readily lifted clear of the lower half of the outer casing for repairs or replacement. Such techniques of maintenance works on rotary flow machines are disclosed for example in U.S. Pat. No. 4,925,363, WO 2008/012195 A1 or WO 2006/103152 A1.
In all known cases it is necessary to insert additional means for supporting the lower inner housing half towards the lower outer housing half for avoiding any damage causing contact while the lower inner housing half will be rotated around the rotational axis into an upper position. So it is a common used technique to insert sliding or rolling bodies between the lower inner and outer casing halves to enable rotation of the lower inner housing half with constant distance from the lower outer housing half. An alternative technique is to insert connection means between the lower inner housing half and the rotor unit which connect the lower inner housing half torque proof to the rotor unit.
A further disadvantage of all known joints between the lower and upper inner housing halves is the fact that all known mounting means in order to support the inner housing to the outer housing do not allow a thermal expansion of the inner housing free of eccentricity, i.e. thermal expansion affects differently on the upper and lower inner housing halves due to mounting arrangements between the inner and outer housing which are arranged adjacent to the split plane which corresponds to the contact plane between the upper and lower inner housing halves.
The document U.S. Pat. No. 7,686,575 discloses a gas turbine with an outer casing and an inner casing with independent thermal expansion of flow path components. The inner casing comprises a first and a second half, the outer casing comprises a first and a second half, the inner casing being mounted within the outer casing on four radially slidable mounts there between, being positioned 90° apart, comprising first and second keys, that are bolted into respective first and second joints between the first and the second half of the inner casing, the first and second keys received in respective first and second slots in respective first and second joints between the first and second halves of the outer casing, each slot being formed as an enclosed chamber except for an open radially inner end thereof that receives the respective key and allows only radial motion of the key.
Another embodiment of a gas turbine that allows relative thermal growth between the inner casing and the outer casing is disclosed in patent application US 2008/0317591.
Another disadvantage of the joints according to the state of the art is that the inner casing is not movable before the upper part of the outer casing has been removed.